Warm air furnace with managed combustion air flow

ABSTRACT

A warm air solid fuel furnace is disclosed that includes a firebox defined by a floor, opposing sides, a top baffle, a front door, and a rear wall, wherein the firebox floor is at least partially lined with fire resistant material. A primary combustion air flow path includes one or more holes through the front door. A secondary air flow path receives air from a front of the furnace and conducts received air along a first opposing side of the firebox, up the rear wall of the firebox, and into at least one tube having orifices, the tube located beneath the top baffle. A rear pilot air flow path receives air from the front of the furnace and conducts received air along a second opposing side of the firebox, up the rear wall of the firebox, and into at least one hole through the rear wall.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a non-provisional of U.S. Patent Application Ser. No. 62/397,081 filed Sep. 20, 2016 entitled “WARM AIR FURNACE WITH MANAGED COMBUSTION AIR FLOW”, the entire disclosure of which is herein incorporated by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

REFERENCE TO SEQUENCE LISTING OR COMPUTER PROGRAM LISTING APPENDIX

Not Applicable

A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the reproduction of the patent document or the patent disclosure, as it appears in the U.S. Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.

BACKGROUND OF THE INVENTION

The present invention relates generally to warm air solid fuel furnaces. More particularly, the present invention relates to solid wood fueled forced air furnaces.

Prior art solid fuel fired warm air furnaces include an inner firebox, an outer cabinet, a flue, circulation blower(s), and limit controls. The firebox is typically configured such that a fire from solid fuel such as wood is built on a set of grates. A baffle or series of baffles are positioned in the flow path of gases produced as the solid fuel is combusted between the fire and the flue of the appliance to slow combustion gases exiting the appliance. These warm air solid fuel fired furnaces were previously exempt from Environmental Protection Agency (EPA) emissions requirements. However, conventional warm air solid fuel fired furnaces produce significant amounts of particulate pollution making these appliances noncompliant with current EPA emissions requirements for Residential Wood Heaters. Warm air solid fuel fired furnaces that are not compliant with EPA emissions requirements can pose a serious health risk when used in a residential setting.

BRIEF SUMMARY OF THE INVENTION

Aspects of the present disclosure provide a warm air solid fuel fired furnace compliant with EPA emissions requirements for Residential Wood Heaters. The furnace can include an improved firebox design incorporating three managed airflows entering the firebox. Primary air provides combustion air at the fuel. Preheated secondary air burns off combustion gases where the secondary air enters the firebox or combustion chamber just below a baffle in the combustion air path. Preheated rear pilot air enters the firebox or combustion chamber at the rear of the firebox or combustion chamber to mix with the primary air and provide complete combustion of the solid fuel.

One aspect of the present disclosure is a warm air solid fuel furnace including a firebox configured to receive wood, said firebox defined by a floor, first and second opposing sides, a top baffle, a front door, and a rear wall, wherein the firebox floor is at least partially lined with fire resistant material. The furnace can include a primary combustion air flow path, wherein the primary air combustion flow path is one or more holes through the front door. A secondary air flow path can be configured to receive air from a front of the furnace and conduct the received air along the first opposing side of the firebox, up the rear wall of the firebox, and into at least one tube having one or more orifices, wherein the at least one tube is located at a top of the firebox beneath the top baffle. A rear pilot air flow path can be configured to receive air from the front of the furnace and conduct the received air along the second opposing side of the firebox, up the rear wall of the firebox, and into at least one hole through the rear wall of the firebox.

In some embodiments, the fire resistant material can be fire bricks, and the fire resistant material can line a rear portion of the firebox floor. In some embodiments, the series of tubes can span laterally across the top baffle, and the orifices can be oriented towards the firebox floor and toward the front of the furnace. In other embodiments, the tubes span distally across the top baffle.

Another aspect of the present disclosure is a warm air solid fuel furnace including a firebox configured to receive wood, said firebox defined by a floor, first and second opposing sides, a top baffle, a front door, and a rear wall, wherein a portion of the firebox floor is lined with fire brick. A primary combustion air flow path can be defined by one or more holes through the front door. A secondary air manifold can be configured to receive air from a front of the furnace and conduct air along a first opposing side of the firebox, up the rear wall of the firebox, and into a series of tubes having orifices, wherein the tubes are located at a top of the firebox below the top baffle. A rear pilot air manifold is configured to receive air from the front of the furnace and conduct air along a second opposing side of the firebox, up the rear wall of the firebox, and into at least one hole defined through the rear wall of the firebox.

In some embodiments, a first inlet through the front of the furnace can be communicated with the secondary air manifold, and a second inlet through the front of the furnace can be communicated with the rear pilot air manifold, wherein secondary air passing through the first inlet and the secondary air manifold and rear pilot air passing through the second inlet and the rear pilot air manifold remain separated until the secondary air and the rear pilot air enter the firebox.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a front view of an embodiment of a warm air solid fuel furnace of the present disclosure.

FIG. 2 is a front cutaway view of the warm air solid fuel furnace of FIG. 1 showing a forced air flow path of the furnace.

FIG. 3 is a side cutaway view at a right side of a firebox of the warm air solid fuel furnace of FIG. 1 showing various air flow paths of the furnace.

FIG. 4 is a top cutaway view of the warm air solid fuel furnace of FIG. 1 showing the various air flow paths of the furnace.

FIG. 5 is a rear cutaway view of the warm air solid fuel furnace of FIG. 1 showing the secondary air flow path and the rear pilot air flow path of the furnace.

FIG. 6 is a detailed cutaway view of an embodiment of a rear wall baffle receiving rear pilot air from the rear pilot air flow path.

Reference will now be made in detail to optional embodiments of the invention, examples of which are illustrated in accompanying drawings. Whenever possible, the same reference numbers are used in the drawing and in the description referring to the same or like parts.

DETAILED DESCRIPTION OF THE INVENTION

While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention and do not delimit the scope of the invention.

To facilitate the understanding of the embodiments described herein, a number of terms are defined below. The terms defined herein have meanings as commonly understood by a person of ordinary skill in the areas relevant to the present invention. Terms such as “a,” “an,” and “the” are not intended to refer to only a singular entity, but rather include the general class of which a specific example may be used for illustration. The terminology herein is used to describe specific embodiments of the invention, but their usage does not delimit the invention, except as set forth in the claims.

As described herein, an upright position is considered to be the position of apparatus components while in proper operation or in a natural resting position as described herein. Vertical, horizontal, above, below, side, top, bottom, and other orientation terms are described with respect to this upright position during operation unless otherwise specified. The term “when” is used to specify orientation for relative positions of components, not as a temporal limitation of the claims or apparatus described and claimed herein unless otherwise specified. The terms “above”, “below”, “over”, and “under” mean “having an elevation or vertical height greater or lesser than” and are not intended to imply that one object or component is directly over or under another object or component.

The phrase “in one embodiment,” as used herein does not necessarily refer to the same embodiment, although it may. Conditional language used herein, such as, among others, “can,” “might,” “may,” “e.g.,” and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements, and/or states. Thus, such conditional language is not generally intended to imply that features, elements and/or states are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without author input or prompting, whether these features, elements and/or states are included or are to be performed in any particular embodiment.

Referring to FIGS. 1-6, a warm air solid fuel furnace 10 according to one embodiment of the invention utilizes three managed airflows entering a firebox 12. The firebox 12 can be configured for receiving solid fuel such as wood, wood chips, coal, etc. In one embodiment, the fuel is cut wood (such as would be used in a fireplace). As shown in FIGS. 2-3, the firebox 12 can be defined by a floor 14, two opposing sides 16 and 18, a top baffle 20, a front door 22, and a rear wall 24. In one embodiment, the firebox floor 14 can be at least partially lined with fire resistant material 17 (e.g., fire brick or ceramic fire board). The firebox floor 14 can also include a grate 15 that is not lined with fire resistant material. The firebox front door 22 can be selectively opened to serve as the fuel loading point for the firebox 12.

An ash tray 26 can be mounted below the grate 15, such that ash can be swept into the ash tray 26 through the grate 15 between uses of the furnace 10. In some embodiments, a rear portion 14 a of the firebox floor 14 can be lined with fire resistant material. The grate 15 can be positioned on a front portion 14 b of the firebox floor 14, such that ash can be raked forward and into the ash tray 26 below the firebox 12. In some embodiments, an ash tray access door 28 can be positioned on the front of the furnace 10 beneath the front door 22 of the firebox 12. The ash tray access door 28 can be selectively opened to provide access to the ash tray 26 for removal and emptying of the ash tray 26 as needed. In other embodiments, the grate 15 can be positioned on the rear portion 14 a of the firebox floor 14 and the front portion 14 b of the firebox floor 14 can be lined with fire resistant material, with the ash tray access door 28 located on a rear side of the furnace 10. In some embodiments, the firebox floor 14 can include an open area positioned above an ash tray 26 without a grate such that ash can be swept directly into the ash tray 26 without passing over a grate.

During use of the furnace, a solid fuel fire can be built on the portion of the firebox floor 14 lined with fire resistant material 17. Primary air 30 is introduced into the firebox 12 through the main firebox door 22. A primary air combustion air flow path 32 can be defined by one or more holes 34 defined through the front door 22 of the firebox 12. Primary air 30 can provide an initial source of air for combusting the solid fuel positioned on the firebox floor 14.

Top baffle 20 is positioned at the top of the firebox 12 and can be positioned above a fire built within the firebox 12. An air plenum 21 can be defined above the top baffle 20, and a flue 23 can be in fluid communication with the air plenum 21. Top baffle 20 can extend from a rear wall 24 of the firebox 12 toward the front of the furnace 10. A gap 25 can be formed between the top baffle 20 and the front of the furnace 10. Air gap 25 can be relatively small in comparison to the length of the firebox 12 and the length of the top baffle 20, such that the top baffle 20 forms a substantial barrier between the firebox 12 and the air plenum 21 above the top baffle 20. The top baffle 20 thus encourages exhaust gas and smoke produced from the combustion of the solid fuel within the firebox 12 to remain in the firebox 12 to produce a more complete combustion of the solid fuel, including further combustion of particulate matter in the smoke or gas produced from the solid fuel. In one embodiment, the top baffle 20 is insulated or lined on a top side of the baffle with fire resistant material (e.g., fire brick or ceramic fiber board) to help retain heat within firebox 12. Exhaust gases and smoke can slowly be emitted from the firebox 12 through the air gap 25 into the air plenum 21, where the flue can receive the exhaust gases and the exhaust gases and smoke can be emitted from the furnace 10 through the flue 23. The flue 23 in some embodiments can be extended or routed through an exterior wall or roof of a residential dwelling such that smoke being emitted from the furnace 10 can escape to an exterior of the residence.

As shown in FIGS. 3-5, secondary air 36 enters the furnace 10 at the front of the furnace 10 and travels through a secondary air manifold 38 from the front of the furnace 10 to the back of the furnace 10, the secondary air manifold 38 positioned on the first opposing side 16 of the firebox 12. In one embodiment, the first opposing side 16 and the secondary air manifold 38 of the firebox 12 are integral with one another.

The secondary air manifold 38 can extend around and up the rear wall 24 of the firebox 12. The secondary air manifold 38 can thus conduct secondary air 36 up the rear wall 24 of the firebox 12 and between the rear wall 24 of the firebox 12 and the secondary air manifold 38. The secondary air 36 can then travel back toward the front of the firebox 10 and into at least one tube 46 including orifices 48, the tube 46 positioned beneath the top baffle 20. Secondary air 36 can be directed into the at least one tube 46 and out the orifices 48. In some embodiments, the secondary air 36 can travel through first and second upper side passages 42 and 44 positioned on opposing sides of top baffle 20, as shown in FIGS. 2-3. In some embodiments, the tube 46 can extend laterally across the top baffle 20 between the first and second side passages 42 and 44. In other embodiments, the at least one tube 46 can extend distally across the top baffle 20. In some embodiments, the at least one tube 46 is a series of tubes 46, each tube 46 including a plurality of orifices 48. In some embodiments, each of the tubes 46 can be spaced equidistantly from the top baffle 20.

In some embodiments, secondary air 36 from the secondary air manifold 38 and side passages 42 and 44 can travel into the series of tubes 46 and out of the orifices 48 into the firebox 12. Each tube 46 can have a first tube end 46 a communicated with the first side passage 42, and a second tubed end 46 b communicated with the second side passage 44, such that secondary air 36 from the secondary manifold 38 can be directed into both ends of the tubes 46. In other embodiments, a single side passage can be defined on the furnace 10 and secondary air 36 can be directed into the tubes 46 and out of the orifices 48 from only one end of the tubes 46. The orifices 48 can be generally oriented to direct secondary air 36 toward the firebox floor 14. The secondary air 36 can thus direct smoke from the solid fuel back toward the fire and the bottom of the firebox 12 for further combustion.

The tubes 46 can be positioned beneath the top baffle 20 and spaced equidistantly beneath the top baffle 20. In some embodiments, the tubes 46 can be directly mounted to the top baffle 20. In other embodiments, the tubes 46 can be suspended beneath the top baffle 20 between first and second side passages 42 and 44. In one embodiment, the top baffle 20 is higher at the front of the furnace 10 than at the rear of the furnace 10, and the orifices 48 on the tubes 46 can be oriented in a downward direction toward the firebox floor 14 and toward the front of the furnace 10.

Thus, as shown in FIGS. 2-5, a secondary air flow path 40 can be defined on the furnace 10 and can be configured to receive air from the front of the furnace 10 and conduct air along the first opposing side 16 of the firebox 12, up the rear wall 24 of the firebox 12, and into a series of tubes 46 having orifices 48, wherein the tubes 46 are located beneath the top baffle 20. In some embodiments, the tubes 46 can span laterally across the top baffle 20 between first and second side passages 42 and 44, and the orifices 48 can be oriented to direct air toward the firebox floor 14 and toward the front of the furnace 10.

Tertiary or rear pilot air 50 enters the furnace 10 through the front of the furnace 10 and travels to the back of the firebox 12 through a rear pilot air manifold 52 on the second opposing side 18 of the firebox 12 and opposite the secondary air 36. In one embodiment, the second opposing side 18 of the firebox 12 and the rear pilot air manifold 52 are integral with one another.

The rear pilot air manifold 52 can extend around and up the rear wall 24 of the firebox 12. The rear wall 24 can include at least one hole 54 defined through the rear wall 24 of the firebox 12, the at least one hole 54 being communicated with the rear pilot air manifold 52 such that rear pilot air 50 can be directed from the rear pilot air manifold 52 through the at least one hole 54 in the rear wall 24 and into the firebox 12. The at least one hole 54 can be located no more than half way up the rear wall 24 of the firebox 12 in some embodiments such that the rear pilot air 50 can be directed into the firebox 12 from the rear pilot air manifold 52 approximately halfway up the rear wall 24 of the firebox 12 through a series of holes in the rear wall 24, as shown in FIG. 2. In some embodiments, the rear wall 24 can be a substantially flat and vertical wall such that rear pilot air 50 can be directed into the firebox 12 in a direction generally toward the front of the furnace 10.

Referring to FIGS. 2-3 and 6, in some embodiments, the rear wall 24 can include a rear wall baffle 56, the rear wall baffle 56 forming a part of the rear pilot air manifold 52. The rear wall baffle 56 can be substantially sealed against the rear wall 24 of the firebox 12. The rear wall baffle 56 can be oriented with a top of the rear wall baffle 56 closer to the front of the furnace 10 than a bottom of the rear wall baffle 56 when the furnace is in an upright position. The at least one hole 54 in the rear wall 24 can be located in the rear wall baffle 56 such that the rear wall baffle 56 is angled with the holes 54 in the rear wall baffle 56 oriented to direct rear pilot air 50 toward at least one of the bottom of the firebox 12 or the firebox floor 14 and the front of the firebox 12. The rear pilot air 50 in some embodiments can further direct smoke from the solid fuel back toward the fire and the bottom of the firebox 12 for further combustion. As shown in FIG. 2, in some embodiments, the rear wall baffle 56 can include a plurality of holes 54 therethrough, the plurality of holes 54 providing increasing flow capacity lower on the rear wall baffle 56 than higher on the rear wall baffle 56. Rear wall baffle 56 is shown in FIG. 2 having an upper and lower row of holes 54, with the lower row of holes including a greater number of holes than the upper row of holes to achieve an increasing flow capacity lower on the rear wall baffle 56.

As shown in FIGS. 2-5, a rear pilot air flow path 60 can thus be defined on the furnace 10, the rear pilot air flow path 60 configured to receive air from a front of the furnace 10 and conduct air along a second opposing side of the firebox 12, up the rear wall 24, and into at least one hole 54 through the rear wall 24 of the firebox 12 to provide rear pilot air 50 to the firebox 12.

A first inlet 62 can be defined through the front of the furnace 10, and a second inlet 64 can be defined through a front of the furnace 10. The first inlet 62 can be communicated with the secondary air manifold 38 and the secondary air flow path 40 and the second inlet 64 can be communicated with the rear pilot air manifold 52 and the rear pilot air flow path 60. Secondary air 36 passing through the first inlet 62 and the secondary air manifold 38 and rear pilot air 50 passing through the second inlet 64 and the rear pilot air manifold 52 remain separated until the secondary air 36 and the rear pilot air 50 enter the firebox 12. In other words, the secondary air flow path 40 and the rear pilot air flow path 60 remain separate and independent of one another until the respective air flow paths reach the firebox 12, such that secondary air 36 entering the first inlet 62 does not mix with the rear pilot air 50 entering the second inlet 64 until the secondary air 36 and the rear pilot air 50 enter the firebox 12.

Keeping the manifolds 38 and 52 and the air flow paths 40 and 60 separate from one another, as well as separate from the primary air path, can help prevent the air flow paths 32, 40 and 60 from negatively interfering with one another and affecting the intake rates of air coming into the respective air flow paths and manifolds during use of the furnace 10. By keeping the air flow paths separate, a flow capacity of the primary air path, a flow capacity of the secondary air path, and a flow capacity of the rear pilot air flow path are independently predetermined to maximize combustion of the wood and combustible gases given off by the wood during combustion.

Secondary air manifold 38 can generally be a passage or network of passages oriented to direct secondary air 36 from the first inlet 62 to the tubes 46 below the top baffle 20, and rear pilot manifold 52 can generally be a passage or network of passages oriented to direct rear pilot air 50 from the second inlet 64 to the at least one hole 54 in the rear wall 24. In some embodiments, each of the secondary air manifold 38 and the rear pilot air manifold 52 can be a single unitary duct, pipe, or chamber extending from the respective inlet to the respective entrance point into the firebox 12. In other embodiments, each manifold can include a combination of multiple ducts, pipes, chambers, etc. extending between and defining an air path from the respective inlet to the respective entrance point into the firebox 12.

The secondary air 36 and the rear pilot air 36 can be heated as the air sources travels through the secondary air manifold 38 and the rear pilot air manifold 52 and along the secondary air flow path 40 and the rear pilot air flowpath 60, respectively, from the front of the furnace 10 to the rear of the furnace 10. In some embodiments, at least a portion of the sides 16 and 18 of the firebox 12 along which the secondary air 36 and rear pilot air 50 respectively travel are not insulated, such as by fire brick or ceramic fire board, from the firebox 12. In other embodiments, the secondary air manifold 38 and the rear pilot manifold 52 can be positioned directly within the firebox 12. In some embodiments, a portion of the sides 16 and 18 of the firebox 12 are lined with fire resistant materials such as fire bricks such that heat transfer from the firebox 12 can primarily occur in the areas of the sides 16 and 18 where the secondary air manifold 38 and the rear pilot air manifold 52 are located, thus helping optimize heat transfer into the secondary air 36 and rear pilot air 50 passing through the furnace 10.

Such configurations allow for the secondary air 36 and rear pilot air 50 to be preheated by the firebox 12 as they pass through their respective manifolds 38 and 52. Heating of the secondary air 36 and rear pilot air 50 can help burn leftover fuel and particulate matter in the smoke being emitted from the primary combustion of the fuel resting on a floor 14 of the firebox 12 as the secondary and rear pilot air 36 and 50 interact with the smoke within the firebox 12. Fire bricks in the floor 14 of the firebox 12 can replace traditional open grates to form a solid bottom or floor 14 for the fuel to sit on. This reduces overall turbulence around the wood (i.e., fuel) during combustion which allows for a more metered air introduction.

The primary, secondary, and rear pilot airstreams, in addition to the fire brick floor 14 for the fuel to rest on (instead of the traditional all grate firebox floor) allow for a combustion air flow balance in the system so that optimal combustion can occur within the firebox 12. This results in reduced overall particulate matter emissions and improved efficiency over traditional warm air furnaces (i.e., more heat delivered to an area to be warmed by the furnace 10 for a given amount of wood burned within the furnace firebox 12).

Referring to FIG. 2, in some embodiments, the furnace 10 can include an inner housing 70. The firebox 12, the secondary air manifold 38, and the rear pilot air manifold 52 can be positioned within the inner housing 70, with smoke and other biproduct from the combusted solid fuel being contained and emitted from the inner housing 70. In some embodiments, one or more of the firebox 12 components, the secondary air manifold 38, or the rear pilot air manifold 52 can form a part of the inner housing 64. In other embodiments, the inner housing 70 can be an entirely separate housing, with the firebox 12, secondary air manifold 38, and the rear pilot air manifold 52 positioned entirely within the inner housing 70.

The furnace 10 can include an outer housing 72 at least partially enclosing the inner housing 70. The outer housing 72 can be spaced from the inner housing to form a forced air passage 76 between the inner housing 70 and the outer housing 72. One or more blower units 74 can be mounted to the outer housing unit 72 and be operable to force air through the forced air passage 76. An exit duct 78 can be communicated with the forced air passage 76, such that the blower unit 74 can force air through the forced air passage and out of the exit duct 78. During use of the furnace 10, as air is forced through the forced air passage 76, the air can be heated by the firebox 12, such that heated air can be emitted from the exit duct 78. In a residential setting, the heated air can exit the duct into a single room, or the heated air can be directed to various rooms within the residence by way of a duct system to condition multiple rooms within the residence.

This written description uses examples to disclose the invention and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

It will be understood that the particular embodiments described herein are shown by way of illustration and not as limitations of the invention. The principal features of this invention may be employed in various embodiments without departing from the scope of the invention. Those of ordinary skill in the art will recognize numerous equivalents to the specific procedures described herein. Such equivalents are considered to be within the scope of this invention and are covered by the claims.

All of the compositions and/or methods disclosed and claimed herein may be made and/or executed without undue experimentation in light of the present disclosure. While the compositions and methods of this invention have been described in terms of the embodiments included herein, it will be apparent to those of ordinary skill in the art that variations may be applied to the compositions and/or methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit, and scope of the invention. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope, and concept of the invention as defined by the appended claims.

Thus, although there have been described particular embodiments of the present invention of a new and useful “WARM AIR FURNACE WITH MANAGED COMBUSTION AIR FLOW” it is not intended that such references be construed as limitations upon the scope of this invention except as set forth in the following claims. 

What is claimed is:
 1. A warm air solid fuel furnace comprising: a firebox configured to receive wood, said firebox defined by a floor, first and second opposing sides, a top baffle, a front door, and a rear wall, wherein the firebox floor is at least partially lined with fire resistant material; a primary combustion air flow path, wherein the primary air combustion flow path is one or more holes through the front door; a secondary air flow path configured to receive air from a front of the furnace and conduct the received air along the first opposing side of the firebox, up the rear wall of the firebox, and into at least one tube having orifices, wherein the at least one tube is located at a top of the firebox beneath the top baffle; and a rear pilot air flow path configured to receive air from the front of the furnace and conduct the received air along the second opposing side of the firebox, up the rear wall of the firebox, and into at least one hole through the rear wall of the firebox.
 2. The furnace of claim 1, wherein: the firebox floor comprises a section that is a grate that is not lined with fire resistant material; and the furnace further comprises an ash tray mounted in the furnace below the grate.
 3. The furnace of claim 1, wherein a first inlet through the front of the furnace to the secondary air flow path is separate from a second inlet through the front of the furnace to the rear pilot air flow path, and secondary air entering the first inlet does not mix with rear pilot air entering the second inlet until the rear pilot air and the secondary air enter the firebox.
 4. The furnace of claim 1, wherein: the rear wall includes a rear wall baffle in communication with the rear pilot air flow path; the at least one hole in the rear wall is defined through the rear wall baffle; and the rear wall baffle comprises a plurality of holes therethrough, the plurality of holes providing increasing flow capacity lower on the rear wall baffle than higher on the rear wall baffle.
 5. The furnace of claim 1, wherein: the rear wall includes a rear wall baffle in communication with the rear pilot air flow path, the at least one hole in the rear wall defined through the rear wall baffle; and a top of the rear wall baffle is closer to the front of the furnace than a bottom of the rear wall baffle such that the at least one hole is oriented to direct rear pilot air toward the floor of the firebox and toward the front of the furnace.
 6. The furnace of claim 1, wherein the fire resistant material is fire brick.
 7. The furnace of claim 1, wherein a top of the top baffle is lined with fire brick.
 8. The furnace of claim 1, wherein the top baffle is higher at the front of the furnace than at a rear of the furnace when the furnace is in an upright position.
 9. The furnace of claim 1, wherein: the top baffle is higher at a front of the furnace than at a rear of the furnace when the furnace is in an upright position; the at least one tube is a series of tubes each having orifices; the orifices in the series of tubes are oriented to direct secondary air from the secondary air flow path into the firebox toward at least one of the floor of the firebox and the front of the furnace; and each tube of the series of tubes is spaced equidistant from the baffle.
 10. The furnace of claim 1, wherein the at least one hole in the rear wall of the firebox is located no more than half way up the rear wall.
 11. The furnace of claim 1, wherein the firebox is configured to preheat secondary air and rear pilot air as the secondary air and rear pilot air move from the front of the furnace to a rear of the furnace along the secondary air flow path and the rear pilot air flow path respectively.
 12. The furnace of claim 1, further comprising: an air plenum positioned above the top baffle; and a gap between the top baffle and a front of the furnace, the gap allowing exhaust gases to pass from the firebox and into the air plenum.
 13. The furnace of claim 12, further comprising a flue in communication with the air plenum, said flue configured to receive exhaust gases.
 14. A warm air solid fuel furnace comprising: a firebox configured to receive wood, said firebox defined by a floor, first and second opposing sides, a top baffle, a front door, and a rear wall, wherein a rear portion of the firebox floor is lined with fire brick; a primary combustion air flow path, wherein the primary air combustion flow path is defined by one or more holes through the front door; a secondary air flow path configured to receive air from a front of the furnace and conduct air along the first opposing side of the firebox, up the rear wall of the firebox, and into a series of tubes having orifices, wherein the tubes are located at a top of the firebox and span laterally across the top baffle, and the orifices are oriented at least partially towards the firebox floor; and a rear pilot air flow path configured to receive air from the front of the furnace and conduct air along the second opposing side of the firebox, up the rear wall of the firebox, and into a plurality of holes defined through the rear wall of the firebox.
 15. The furnace of claim 14, wherein: each of the tubes in the series of tubes has a first and second end; and secondary air from the secondary air flow path is directed into both ends of the series of tubes.
 16. The furnace of claim 14, wherein the secondary air flow path and the rear pilot air flow path are separate and independent from one another within the furnace until the respective air flow paths reach the firebox such that a flow capacity of the primary air path, a flow capacity of the secondary air path, and a flow capacity of the rear pilot air flow path are independently predetermined to maximize combustion of the wood and combustible gases given off by the wood during combustion.
 17. The furnace of claim 14, further comprising: an inner housing, wherein the firebox, the secondary air flow path, and the rear pilot air path are positioned within the inner housing; an outer housing at least partially enclosing the inner housing, a forced air passage formed between the inner housing and the outer housing; an exit duct defined on the outer housing, the exit duct in fluid communication with the forced air passage; and a blower unit mounted to the outer housing, the blower unit configured to force air through the forced air passage and out of the exit duct.
 18. The furnace of claim 17, wherein the firebox is configured to transmit heat to the air forced through the forced air passage by the blower unit.
 19. A warm air solid fuel furnace comprising: a firebox configured to receive wood, said firebox defined by a floor, first and second opposing sides, a top baffle, a front door, and a rear wall, wherein a portion of the firebox floor is lined with fire brick; a primary combustion air flow path defined by one or more holes through the front door; a secondary air manifold configured to receive air from a front of the furnace and conduct air along a first opposing sides of the firebox, up the rear wall of the firebox, and into a series of tubes having orifices, wherein the tubes are located at a top of the firebox below the top baffle; and a rear pilot air manifold configured to receive air from the front of the furnace and conduct air along a second opposing side of the firebox, up the rear wall of the firebox, and into at least one hole defined through the rear wall of the firebox.
 20. The furnace of claim 1, further comprising: a first inlet through the front of the furnace communicated with the secondary air manifold; and a second inlet through the front of the furnace communicated with the rear pilot air manifold; wherein secondary air passing through the first inlet and the secondary manifold and rear pilot air passing through the second inlet and the rear pilot air manifold remain separated until the secondary air and the rear pilot air enter the firebox. 